Generally, there are three liquid droplet injection designs capable of ejecting liquid droplet with uniform droplet size, which are thermal bubble inkjet printhead, electrostatic inkjet printhead and piezoelectric inkjet printhead. The present invention will focus on the electrostatic inkjet printhead and piezoelectric inkjet printhead that have the ability to eject liquid droplet without using a thermally driven bubble.
Refer to FIGS. 1A, 1B and 1C, which are schematic diagrams showing successive actions of an electrostatic inkjet printhead of side-shooter design. The printhead 100 adopts the side-shooter design in which the nozzle 110 of the printhead 100 being disposed between substrate 120 and substrate 130 is arranged at a side of an electrostatic actuator 140. As seen in FIG. 1A, the electrostatic actuator 140 is kept in a designated position while the printhead 100 is inactive, and the same time that the chamber 150 formed between the substrate 120 and the electrostatic actuator 140 along with the ink reservoir 160 are filled with ink which flow therein through the ink inlet 170 of the printhead 100.
As seen in FIG. 1B, the electrostatic actuator 140 is distorted downward by the action of the electrostatic attraction while the printhead is activated and ready for ink ejection. As the electrostatic attraction disappears, the distorted electrostatic actuator 140 restores that causes the pressure in the chamber 150 to increase rapidly and enables the ink to be ejected from the nozzle 110.
However, the shortcoming of the printhead 100 is that while the ink in the chamber 150 is being ejected from the nozzle 110, it is also being push to flow back to the ink reservoir 160 as seen in FIG. 1C. In this regard, the backward flow ink will affect the refill speed of the chamber 150 since it is blocking the way for the ink to refill the chamber 150. Therefore, the ejection frequency of the printhead 100 has much to be improved.
Please refer to FIGS. 2A, 2B and 2C, which are schematic diagrams showing successive actions of a electrostatic inkjet printhead of top-shooter design. The printhead 200 of FIG. 2A is similar to the printhead 100 of FIG. 1A, which is composed three substrates 220, 230, and 235, wherein a ink reservoir 260 and an actuator 240 are disposed on the substrate 230, and a nozzle 210 is formed directly on the substrate 220 that is arranged on top of the actuator 240.
While the printhead 200 is inactive and the switch 275 is connected to an off position, the actuator 240 formed of a flexible piezoelectric crystal is kept in a designated position as seen in FIG. 2A. When the switch 275 is on, the actuator 240 is distorted downward by the stimulation of a voltage source as seen in FIG. 2B. As the voltage disappears by switching off the switch 275, the distorted actuator 240 restores that causes the pressure in the chamber 250 corresponding to the actuator 240 to increase rapidly and enables the ink to be ejected from the nozzle 210.
The shortcoming of the printhead 200 is the same as that of the printhead 100. The restoring of the distorted electrostatic actuator 240 not only ejects ink in the chamber 250 from the nozzle 210, but also push it to flow back to the ink reservoir 260 such that the backward flow ink will affect the refill speed of the chamber 250 since it is blocking the way for the ink to refill the chamber 250 in addition, the printhead of top-shooter design will suffer the emergence of satellite droplets.
In view of the above description, the present invention provides an inkjet printhead and process for producing the same, capable of eliminating the emergence of satellite droplets while maintaining a high frequency response.